Field of the Invention
The present invention relates to a vertical alignment liquid crystal display apparatus which is driven by multiplex driving.
Description of the Background Art
A liquid crystal display apparatus is broadly used as an information display unit in various electronic devices for consumer or automobile use. In General, a liquid crystal display apparatus is configured by disposing a liquid crystal layer made of a liquid crystal material between two substrates that are placed opposite each other with a gap of roughly several micrometers. As one type of this kind of liquid crystal display apparatus, a vertical alignment liquid crystal display apparatus is known.
In the vertical alignment liquid crystal display apparatus, multiplex driving is used, for example, in order to achieve a dot matrix display. When multiplex driving is conducted, even when the number of scanning lines (the number of common electrodes) is increased, in order to maintain the display quality, a steeper electro-optical characteristics is required. In this regard, for example, Japanese Patent Laid-Open No. 2005-244254 (Patent Document 1) discloses that in order to achieve a favorable steepness, setting the pretilt angle as close to 90° as possible is effective.
Meanwhile, in the foregoing vertical alignment liquid crystal display apparatus, there are cases where a decrease in display uniformity occurs mainly to pixels in a bright state. And this phenomenon is particularly notable in a high temperature environment. The present inventors studied this phenomenon and confirmed that this is caused by the irregular occurrence of unexpected dark regions around the center and not including the edges of the pixels in a bright state. Such dark regions is considered to occur due to the liquid crystal molecules included in the liquid crystal layer aligning to the different direction from the direction regulated by the alignment film.
The disadvantage described above may be eliminated by the liquid crystal display apparatus disclosed in Japanese Patent Laid-Open No. 2012-98333 (hereinafter referred to as Patent Document 2). Specifically, the liquid crystal display apparatus of this precedent is comprised of strip-shaped upper and lower electrodes wherein a pixel is configured in the region where the extending directions of the respective electrodes intersects, and the alignment direction of the liquid crystal layer is set so that the alignment direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer does not become orthogonal to one of the edges of the upper/lower electrodes.
Moreover, the disadvantage described above may be eliminated by the liquid crystal display apparatus disclosed in Japanese Patent Laid-Open No. 2012-93578 (hereinafter referred to as Patent Document 3). Specifically, the liquid crystal display apparatus of this precedent is comprised of upper and lower electrodes wherein the edges of one electrode are formed into bending shapes and a pixel is configured in the region where the extending directions of the respective electrodes intersects, and further the alignment direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer is set parallel to the other electrode. In other words, the alignment direction of the liquid crystal layer is set so that the alignment direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer does not become orthogonal to one of the edges of the upper/lower electrodes.
However, according to the liquid crystal display apparatus disclosed in Patent Document 2, in a case where an (often employed) arrangement wherein one of the strip-shaped upper/lower electrodes is made to correspond to the up-down direction and the other is made to correspond to the left-right direction of the display surface of the liquid crystal display apparatus is adopted, the orientation direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer needs to be set in a direction that deviates from the up-down direction of the display surface. While it is effective to eliminate a decrease in the display uniformity described above by further increasing the deviation of the orientation direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer from the up-down direction of the display surface, asymmetry occurs in the visual angle dependencies during a bright display in the left-right direction of the liquid crystal display apparatus, making such increased deviation not preferred.
Further, according to the liquid crystal display apparatus disclosed in Patent Document 3, it is effective to eliminate a decrease in the display uniformity described above by further increasing the angle formed by the edge of one of the upper/lower electrodes and the orientation direction of the liquid crystal molecules at the substantial center in the layer thickness direction of the liquid crystal layer, but to do so requires further increase of the angle at which the edge of the electrode bends.
Increasing the angle at which the edge bends, however, makes the shape of the bent edge noticeably discernable in appearance, and therefore is not preferred.